Elastomers based on the condensation of a major proportion of thiodiethanol with one or more aliphatic diols containing a vulcanizable double bond are described by Aloia, U.S. Pat. No. 3,951,927; Chang et al., U.S. Pat. No. 3,985,708; Chang, U.S. Pat. No. 4,000,213; Li et al., U.S. Pat. No. 4,028,305, all of which are incorporated herein by reference. Heretofore, application of conventional sulfur vulcanization systems, e.g., sulfur, zinc oxide, benzothiazole sulfenamides, thiuram sulfides, mercaptobenzothiazole, and the like, to the vulcanization of these vulcanizable elastomers of thiodiethanol has been less than satisfactory. Zinc oxide has heretofore been considered essential to the sulfur vulcanization of unsaturated elastomers. In the thiodiethanol-based elastomers of the present invention, conventional sulfur vulcanization systems which include zinc oxide result in a fast cure, but the resulting vulcanized elastomer exhibits extremely poor heat aging properties, as manifested by high compression set and poor continuous stress relaxation. However, when zinc oxide is omitted, the cure rate is impractically slow. All of these factors indicate a poor vulcanization system for polythiodiethanol elastomers.
In order for an elastomer to achieve commercial success, it must be vulcanizable to useful products with an efficient, practical vulcanization system. It is an object of this invention to provide such a system. It is also an object to provide useful vulcanized products from thiodiethanol-based elastomers, and to provide elastomers having significantly improved compression set properties.